| 研究実績の概要 |
During the last year, 6 new oxyhydrides compounds have been prepared: LnHO with Ln = Sm, Gd, Tb, Dy, Ho, and Er. Their conductivities and the ammonia synthesis catalytic activity have also been estimated. Two novel high-pressure polymorphs of lanthanum oxyhydride have been successfully predicted and stabilized under pressure. High-pressure synthesis offers an access to new compounds that exhibit novel chemical and physical functions. When reacted at 3 GPa, the fluorite structure of LaHO with anion-centered tetrahedral (HLa4/OLa4) geometry is transformed to the PbCl2-type structure involving coordination number increase of H- to five (HLa5 square pyramids). Upon further application of pressure to 5 GPa, LaHO changed into the anti Fe2P-type structure. This fact underlines the role of multiple anions with distinct compressibility for the realization of unique anion-coordination reversal.
So far, two papers have been submitted and accepted in the Journal of American Chemical Society.
T. Broux, et al., Chemical pressure-induced anion order-disorder transition in LnHO enabled by hydride size flexibility, J. Am. Chem. Soc. 2018, 140, 11170-11173
T. Broux, et al., High-pressure Polymorphs of LaHO with Anion Coordination Reversal
J. Am. Chem. Soc. 2019, accepted
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| 今後の研究の推進方策 |
In the future, we want to extend the anionic composition of these materials and search for high-pressure polymorphs to divalent cations such Ca, Ba, etc… We believe that this study can be extended to other oxyhydrides and more generally hydride-fluorides and hydride-nitrides. Since high pressure phases of CaF2 have been theoretically predicted to be excellent ionic conductors, 23,32 α-LaHO, γ-LaHO and δ-LaHO may also be a potential candidate for hydride conductors, possibly after introduction of appropriate anion vacancy by aliovalent cation substitution. Higher-pressure study is also of great interest. AIRSS searches on LaHO up to 100 GPa has predicted a further transition to a hexagonal (P63/mmc) structure with HLa5 bipyramidal and OLa6 octahedral coordination
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